No description available.

In many areas of the Western U.S., diffuse knapweed (Centaurea diffusa Lam.) has invaded into plant communities dominated by bluebunch wheatgrass (Pseudomegnaria spicata [Pursh] A. Love). The objectives of this study were to compare growth response of both species when grown under altered moisture and temperature regimes while in the seedling stage and to further elucidate the competitive ability of diffuse knapweed compared to bluebunch wheatgrass. Isolated individuals were grown in four different environmental chamber conditions (12 hr day length, 10 and 16C and -0.01 MPa and -0.03 MPa soil moisture). Diffuse knapweed penetrated quicker than bluebunch wheatgrass starting on day 20, regardless of temperature and moisture and knapweed penetration was greatest under warm and wet soil conditions. Bluebunch wheatgrass developed more root length initially under warmer and drier conditions, but those differences diminished after thirty days growth. Warmer and wetter soil conditions favored diffuse knapweed leaf area production in later stages of seedling growth. Diffuse knapweed had more rapid root penetration than bluebunch wheatgrass under the conditions studied. Diffuse knapweed maximized shoot production, indicative of a relatively fast growing species, while bluebunch wheatgrass maximized root production, characteristic of a relatively slow growing species. Diffuse knapweed seedlings grew best under warmer and wetter conditions. Comparing plant efficiency (indices of plant efficiency based on the measurement of a plant attribute divided by the total biomass of the plant), diffuse knapweed was apparently more efficient than bluebunch wheatgrass at producing the competitive attributes of root penetration, leaf area and root length. / Graduation date: 1998